1. Field of the Invention
The present invention relates to a fuel injection device. The present invention can be suitably applied to a fuel injection device mounted to each cylinder of an internal combustion engine for injecting fuel into the cylinder.
2. Description of Related Art
A fuel injection valve of a fuel injection system of a diesel engine is known as a fuel injection device. The fuel injection valve is mounted to each cylinder of the engine and injects fuel into a combustion chamber of the cylinder. The fuel injection valve includes a nozzle body, which is formed with injection holes for injecting the fuel, and a nozzle needle, which ascends and descends inside the nozzle body to open and close the injection holes, as described in Unexamined Japanese Patent Application Publication No. 2003-83203. In this kind of fuel injection valve, the nozzle needle has a sliding portion in the shape of a circular column, which can move in the nozzle body in a sliding manner, an insertion portion in the shape of a circular column, of which external diameter is smaller than that of the sliding portion, and a pressure-receiving portion connecting the sliding portion with the insertion portion. The nozzle body is formed with a guide portion, which holds the sliding portion in a sliding manner, and with a fuel sump chamber, which is formed on an injection hole side of the guide portion. The insertion portion is inserted through the fuel sump chamber.
High-pressure fuel, which is to be injected through the injection holes, is supplied to the fuel sump chamber. The high-pressure fuel leaks through a clearance between the sliding portion and the guide portion.
A fuel injection valve of a common rail type fuel injection system as a fuel injection system of a diesel engine disclosed in Unexamined Japanese Patent Application Publication No. 2003-166457 includes a nozzle needle, a nozzle body, a body for holding the nozzle body, and a command piston. The command piston reciprocates inside the body to directly or indirectly move the nozzle needle. A control chamber is formed on a side of the command piston opposite from the nozzle needle. The fuel pressure in the control chamber can be changed by opening or closing an electromagnetic valve. When the electromagnetic valve is closed, the high-pressure fuel is supplied into the control chamber, and the control chamber is filled with the high-pressure fuel. A sliding portion of the command piston and a guide portion of the body can slide on each other. When the control chamber is filled with the high-pressure fuel, the high-pressure fuel leaks through the clearance between the sliding portion of the command piston and the guide portion of the body.
The sliding portion of the nozzle needle, the guide portion of the nozzle body and the fuel sump chamber constitute an in-high-pressure-oil sliding part for storing high-pressure hydraulic oil inside. The sliding portion of the command piston, the guide portion of the body and the control chamber constitute another in-high-pressure-oil sliding part for storing the high-pressure hydraulic oil inside.
As shown in FIG. 6, in the in-high-pressure-oil sliding part, an inner periphery of the guide portion 12 on the fuel sump chamber 16 side is enlarged by deformation due to the high-pressure fuel stored in the fuel sump chamber 16. Accordingly, a clearance 451 between the inner periphery of the guide portion 12 and the sliding portion 32 of the nozzle needle on the fuel sump chamber 16 side is enlarged. Therefore, the fuel leak quantity increases as the fuel pressure increases.
In the above structure of the related art having the in-high-pressure-oil sliding part shown in FIG. 6, there is a possibility that the sliding portion 32 of the nozzle needle on a low-pressure side contacts the guide portion 12 of the nozzle body, and a pressure between the contacting surfaces of the sliding portion 32 and the guide portion 12 increases if the guide portion 12 is deformed by the high-pressure fuel. Therefore, there is a possibility that at least one of the sliding portion 32 of the nozzle needle on the low-pressure side (in an area A in FIG. 6) and the guide portion 12 of the nozzle body facing the sliding portion 32 on the low-pressure side (in the area A in FIG. 6) is abraded.
As a result, the clearance between the sliding portion 32 and the guide portion 12 will enlarge and the fuel leak quantity will increase.
In the technology of the related art having the command piston, the long command piston is reciprocated by changing the pressure in the control chamber, of which pressure is changed by opening or closing the electromagnetic valve. Therefore, there is a possibility that the clearance between the command piston and the body enlarges and the fuel leak quantity further increases.